Abstract
π-Extended conjugation offers the opportunity to unveil new frontiers in materials, coupling redox activity with tunable photophysical properties. Here, we report a new family of π-conjugated salen ligands bearing phenylene bridges and tunable substituents, together with their corresponding boron difluoride complexes. Owing to the extended π-delocalization, these new compounds show promising results in electrochemical CO2 reduction to CO, achieving a remarkable Faradaic efficiency for an organocatalyst (up to 56%). Electrochemical, spectroscopic, and computational analyses support a ligand-centered mechanism in which single-electron reduction activates the framework for CO2 binding at the imine nitrogen, forming an N-bound CO2H intermediate. Beyond electrocatalysis, coordination to boron rigidifies the π-framework, producing emissive boron-salphen complexes with large Stokes shifts (>7000 cm−1). These complexes function as efficient photosensitizers for singlet-oxygen generation, enabling mild oxidative cleavage of alkenes under blue-light irradiation. This work demonstrates that π-extension transforms the traditional salphen framework into a redox-active engine for small-molecule activation, bypassing the need for transition metals in CO2 electroreduction while simultaneously unlocking good photosensitizing capabilities.